Automotive Engine Rebuilder Improves Quality with Flexible Honing Tool

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Rebuilt engines experience less engine failure after unique cylinder hone operation

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RMP, a Holman Enterprise (Pennsauken, NJ), a remanufacturer of car and truck engines and related parts, has pioneered a metal finishing system that improves the quality of the surface lining in the cylinders of its rebuilt engines. The new method incorporates a special engine hone used to finish the cylinder wall after it has undergone a rigid honing operation.

Results indicate that the company’s rebuilt engines have experienced less engine failure due to improper seating of piston rings with poorly finished cylinder wall as result of using the honing tool.

In the past, RMP was honing the engine cylinders with a standard rigid honing machine, but found that the surface finish did not meet the company’s set of specifications. The engines’ cylinders range from 6 in. to 7 in. in depth and from 3 in. to 5 in. in diameter.

According to Dale Houghton, RMP’s engine department supervisor, the cylinder walls of the engines were receiving a peaky finish, with cut, torn and folded metal remaining along the cylinders’ surface. This type of finish, he noted, could eventually lead to engine failure. This problem could begin during the break-in period of the newly rebuilt engine when the peaky finish could adversely coact with the piston rings.

The principal of coacting metals states that the pressure on the surface of the cylinder wall is equal to the load divided by the projected bearing area. For example, if there is a pressure of 500lb./sq. in. on the lower surface of two coacting metals and, in theory, both surfaces are flat, the pressure on the surface is 500 lb./sq. in. Since no surface is perfectly smooth, there is bound to be some abrasion between the surfaces of the cylinder walls and piston rings. If the surface has an 80% smooth, or plateaued, finish, the pressure is 625lb./sq. in. If the surface is 10% plateaued, the pressure becomes 5000lb./sq. in., leading to severe engine damage.

Looking for a solution to its surface finishing problem, RMP turned to Brush Research Manufacturing Co., Inc. (Los Angeles, CA), which supplied the company with a novel engine hone known as Flex-Hone. This honing tool consists of a resilient-based hone with abrasive laminated to the ends of high-density nylon filaments. At RMP the honing tool is placed in a hand-held air tool and secured by a standard key chuck.

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Heather Fowlie
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